In manufacturing semiconductor devices, contact holes may be formed in a silicon oxide film. Further, as the semiconductor devices have been miniaturized, a SAC (Self-Aligned Contact) technique has been used to form the contact holes.
The SAC technique is to form contact holes in a silicon oxide film provided between, for example, two gates. To be specific, a silicon nitride film covering two gates is formed between the gates and a silicon oxide film. Since the silicon nitride film serves as an etching stop layer, a contact hole is formed in a self-aligned manner in the silicon oxide film provided in a region between the two gates. In such a SAC technique, generally, plasma of a fluorocarbon gas is used for etching the silicon oxide film, as described in Patent Document 1.
Patent Document 1: Japanese Patent Laid-open Publication No. 2000-307001
In manufacturing semiconductor devices by using the above-described SAC technique, a region formed of silicon oxide may be selectively etched with respect to a region formed of silicon nitride. However, not only the region formed of silicon oxide but also the region formed of silicon nitride is etched by plasma of a fluorocarbon gas. By way of example, in the conventional SAC technique, when a silicon nitride film is exposed by etching a silicon oxide film, the silicon nitride film may also be etched.
Therefore, in selectively etching the region formed of silicon oxide, it becomes necessary to suppress the region formed of silicon nitride from being etched.